1. Field of the Invention
The present invention relates to computer modeling of pollution control devices, and particularly to a computer-implemented method for estimating corona power loss in a dust-loaded electrostatic precipitator.
2. Description of the Related Art
During the 20th century, the world witnessed vast industrial and urban development, which affected positively the standard of life of human beings. However, enormous types of waste in tremendous quantities were generated as a side effect of this development. Particulate emissions are definitely among the industrial waste that needs control. Fly ash is one of the residues generated in the combustion of coal. Fly ash is generally captured from the chimneys of coal-fired power plants, and is one of two types of ash that jointly are known as coal ash. Electrostatic precipitators are one of the most commonly used particulate control devices for collecting fly ash emissions from boilers, incinerators and many other industrial processes.
The basic principles governing the operation of electrostatic precipitators are relatively straightforward, and hence are well described in the literature. The most common geometry for an electrostatic precipitator is the wire-duct or wire-plate electrostatic precipitator (WDEP). A wide range of factors determines the performance of electrostatic precipitators. For optimum design of electrostatic precipitators, it is essential to determine the electric field, current density and hence the coronas power loss and, finally, the collection efficiency.
Theoretical (as well as experimental) analysis in WDEP has received the attention of several investigators. Many of the models reported depend on numerically solving the main system of equations describing the precipitator geometry with a certain choice of boundary conditions. Some models neglect the effect of particle space-charge density and others include it. The charge simulation method has been used to model the electrical characteristics of wire-tube electrostatic precipitators. Such a study involves the evaluation of the electric field, voltage, and charge density distributions in the presence of mild corona quenching. Success has been achieved in the use of the charge simulation method to model the electrical characteristics of cylindrical type electrostatic precipitators in the presence of dust loading. A modified numerical method for calculating the ion and particle charge density, the electric field intensity, and consequently the ion and particle current density in a WDEP has been proposed.
The characteristics of a WDEP have been predicted by combining the method of characteristics and the boundary element method (BEM). In this work, the effect of particle charge density on the precipitator modeling is ignored. Cristina and Feliziani proposed a procedure for the numerical computation of the electric field and current density distributions in a “DC” electrostatic precipitator in the presence of dust, taking into account the particle size distribution. Talaie proposed a model for the prediction of electric field strength distribution and voltage-current characteristics for a high-voltage wire-plate configuration. Ignoring the effect of particle movement and fluid flow, the results of the electrical part of the mathematical model are in good agreement with experimental data.
Zhang et al studied the collisions between charged particles and the collecting plate in a wire-plate electrostatic precipitator (ESP). An experimental study of trace metal emissions from a 220 MW coal fired power plant and a 6 MW fuel oil-based power plant was carried out by Reddy et al. Results of the measurements of the size distribution of seed particles after their precipitation in a wire-plate-type ESP with seven wire electrodes has been investigated by Kocik et al. Nikas et al studied the impact of the ionic wind on the gas flow and its influence on the particle transverse transport velocities in WDEP. The numerical results show the development of cross stream vortices due to ionic wind, with their magnitude depending on the applied wire-to-plate voltage.
Upwind (or downwind) finite difference scheme has been proposed by Lei et al for the calculation of the three-dimensional distributions of the electric potential and the space charge in a wire-plate electrostatic precipitator. Numerical calculations and experimental investigations of gas-particle flows involving an electrical field, as they are found in the electrostatic precipitation process, has been reported by Bottner.
Jedrusik et al. investigated the influence of the physicochemical properties (chemical composition, particle size distribution and resistivity) of the fly ash on the collection efficiency. For this purpose, three electrodes with a difference in design were tested. Under dust-free conditions, simultaneous solution for the governing Poisson's and current continuity equations of WDEP using a combined Boundary Element and Finite Difference Method over a one-quarter section of the precipitator has been reported by Rajanikanth. Xiangrong et al. presented the zero flux boundary condition for the turbulent mixing diffusion model at the wire plane of a wire-plate electrostatic precipitator.
Anagnostopoulos presented a numerical simulation methodology for the calculation of the electric field in wire-duct precipitation systems using finite differencing in orthogonal curvilinear coordinates to solve the potential equation. Neimarlija et al. used the finite volume discretization of the solution domain as a numerical method for calculating the coupled electric and space-charge density fields in WDEP. An unstructured cell-centered second order finite volume method has been proposed for the computation of the electrical conditions by Long et al.
In an experimental study, Miller et al. investigated the impact of different electrode configurations on the precipitator efficiency. Zhuang et al. presented experimental and theoretical studies for the performance of a cylindrical precipitator for the collection of ultra fine particles (0.05-0.5 μm). For particles of the size (0.01-0.1 μm), Ohyama et al. proposed a numerical model for calculation of the WDEP efficiency. For a cylinder wire plate electrode configuration, Dumitran et al. estimated the electric field strength and ionic space charge density.
Talaie et al. proposed a computational procedure to evaluate the voltage current characteristics in WDEP under positive and negative applied voltages. The model took the effect of particle charge into consideration and makes it possible to evaluate the rate of corona sheath radius augmentation as a result of increasing the applied voltage. Measurements of the mass collection rates along a pilot WDEP in an industrial environment has been made by Bacchiega et al. Long et al. used the unstructured finite volume method to compute the three-dimensional distributions of electric field and space charge density. Kim and Lee designed and tested a laboratory scale WDEP. Comparison with existing theoretical models has been made. The study investigated the effect of turbulent flow and the magnitude of rapping acceleration on the collection efficiency.
In computing the ionic space charge and electric field of WDEP, Beux et al. proposed a semi-analytical procedure, based on the Karhunen-Loeve (KL) decomposition to parameterize the current density field. The impact of fly ash resistivity and carbon content on the performance of WDEP has been investigated by Barranco et al.
Thus, in spite of the foregoing analyses, a system and method for estimating corona power loss in a dust-loaded electrostatic precipitator solving the aforementioned problems is desired.